What Are the Ways Joints Are Affected?

Psoriatic arthritis (PsA) is a chronic, inflammatory disease that can range from mild joint inflammation to disabling arthritis that impairs quality of life and function. PsA has distinctive clinical features that are generally divided into five physical domains:

• Skin and nails
• Arthritis affecting the outer most joints, like the fingers and toes, called peripheral arthritis
• Arthritis affecting the spine, called axial disease
• Swelling of the fingers or toes in a “sausage-like” appearance, called dactylitis
• Inflammation at the points where the tendons or ligaments attach, called enthesitis ¹

The bones, while appearing fixed, are living tissues that naturally go through a process of growth and loss. PsA can affect the normal bone process, leading to both an abnormal increase in the loss of bone, called bone resorption, as well as an abnormal growth of bone. This disease process can cause disfigurement and disability.^1,2

How joints are affected by PsA

In some people, PsA only affects a few joints. In others, PsA affects many joints in the body. The wide variation in how the disease appears in different people is part of what makes diagnosis a challenge. Experts categorize the joint involvement in PsA as:

• Oligoarticular – “Oligo” means few. Oligoarticular PsA affects only a few joints, generally less than or equal to four.^1,3 Large joints, hands, or feet can be involved, and this pattern usually occurs in men.³
• Polyarticular symmetric/asymmetric – “Poly” means many. Polyarticular PsA affects more than four joints and can affect both sides of the body (symmetric) or just affect one side of the body (asymmetric).^1,3
• Distal interphalangealpredominant (DIP) – PsA may concentrate in the joints of the fingers or toes. This form of PsA is more likely to have nail involvement.¹ DIP may be symmetric or asymmetric and may affect a few joints or many. It commonly leads to progressive bone destruction.³
• Axial disease, also called spondylitis – PsA can impair the joints between the vertebrae in the spine.¹
• Arthritis mutilans – The most severe form of PsA, arthritis mutilans is characterized by the destruction of the bony tissue in the distal joints, causing deformed shortening of the fingers or toes. ^1,3,4 Arthritis mutilans occurs in up to 5% of PsA cases.³

Some patients with PsA start out with only a few joints affected (oligoarticular) and progress to many joints affected (polyarticular) over time.¹ With effective treatment, some patients with polyarticular disease may become oligoarticular.³ There are few clinical studies that have addressed the clinical presentation of PsA in patients, but one such study found that of 129 early PsA patients, 60% had polyarticular disease and 40% had oligoarticular disease at diagnosis.⁵

Inflammation of joint fluid

Between some bones that come together in a joint is a capsule of fluid that acts as a lubricant, called the synovial fluid. In people with PsA, the synovial fluid in larger joints, such as knees, hips, shoulders, elbows, or wrists, can become inflamed, causing additional pain and stiffness in the joint. When PsA affects the synovial tissue, there is an increase in immune system cells, particularly white blood cells (T-cells, B-cells, and some macrophages) which is a sign of chronic inflammation.¹ While there are no specific diagnostic tests for PsA, one abnormality that can be definitively tested is increased presence of elevated lymphocytes in the synovial fluid.^1,2,6

Joints affected by PsA:

• Fingers and toes
• Foot
• Knees
• Hips

Fingers and toes

Dactylitis, or "sausage-shaped" fingers and toes, occurs in up to 50% of patients with PsA and is a marker of disease progression.  Symptoms include stiffness, especially first thing in the morning or after a period of rest, pain when moving fingers and toes, and reduced range of motion.

How does PsA affect the feet?

Initial symptoms of PsA in the feet include pain, swelling, warmth, and stiffness. Walking can become difficult with stiffness and swelling.  Plantar fasciitis and Achilles tendonitis may also develop which may complicate the isolation of joint problems in the foot.

How does PsA affect the knees?

Symptoms of PsA in the knees include stiffness, especially first thing in the morning or after a period of rest, joint pain, swelling, and reduced range of motion. One or both knees may be affected in a person with PsA. PsA is frequently asymmetrical, affecting only one side of the body. For example, PsA may involve the right knee while the left knee is unaffected. PsA can also be symmetrical, affecting both sides of the body, such as both legs at the same time.

How does PsA affect the hips?

The hips are not frequently affected in most people with PsA. It is estimated that the hips become inflamed due to PsA in less than 10% of cases. People who have the onset of PsA symptoms before age 30 seem to be at the greatest risk for hip involvement, especially if they have spinal involvement. Pain in the hip joint may radiate outward and also include pain in the groin, outer thigh, or buttocks.  Inflammation affecting the hips may cause stiffness, and affect the range of motion, making it difficult to walk without a limp.